The proposed project is designed to examine the neural mechanisms underlying the ontogeny of cerebellar learning using short delay and trace eyeblink conditioning procedures. Previous findings from this projected showed that the ontogeny of delay eyeblink conditioning is highly correlated with developmental changes in the induction of neuronal plasticity within the cerebellum. A substantial body of evidence now indicates that the development of auditory input to the pontine nuclei plays a critical role in the ontogeny of cerebellar learning. The current proposal significantly extends these findings to elucidate the nature of developmental changes in auditory input to the pontine nuclei in Aim 1. It will also test the more general hypothesis that cerebellar learning depends on the development of sensory input to the pontine nuclei, not on the development of cerebellar plasticity mechanisms in Aim 2. That is, the cerebellum is capable of learning early in development but only with early developing sensory systems (olfactory, gustatory, and somatosensory), whereas cerebellar learning emerges later when late developing sensory systems (auditory and visual) are used. The scope of the project will be extended to examine the development of mechanisms underlying trace eyeblink conditioning, a cerebellar learning paradigm that requires the hippocampus and cortical projections to the pontine nuclei (Aim 3). New methods for recording neuronal activity in rat pups with moveable tetrodes will be used to examine the development of thalamic, pontine, and hippocampal activity during eyeblink conditioning. Nothing is known currently about the ontogeny of learning -related activity in the thalamus or hippocampus. Thus, the findings of these experiments will be novel and significant.